1. Field of the invention
The present invention relates to a solid electrochemical element, which includes an ion conductor and the constituent members of which are all solid, such as a solid cell, a solid electrical double layer capacitor, a solid electrochromic display or the like, as well as to a process for producing said element.
More particularly, the present invention relates to a solid electrochemical element with excellent mechanical strength and excellent environmental resistance which is constituted by (a) an ion conductor comprised of a solid electrolyte and an insulating supporting substance, such as a plastic resin or the like, and having flexibility and excellent environment resistance, and (b) an electrode material in particulate form, as well as to a process for producing said element.
2. Description of the Related Art
Solid electrochemical elements whose constituent members are all solid are advantageous in that they have no problem of liquid leakage and they can be easily produced in a small and thin shapes. In constituting such an element, there is required a solid ion conductor for moving ions within the element, namely, a solid electrolyte. The solid electrolyte is classified by the type of movable ion, such as Li.sup.+ -conductive solid electrolyte, Ag.sup.+ -conductive solid electrolyte, Cu.sup.+ -conductive solid electrolyte, H.sup.+ -conductive solid electrolyte, etc. A solid electrochemical element is constituted by combining one of these solid electrolytes with an appropriate electrode material.
Not only solid electrolytes, but also electrolytes in general have no directional property or no anisotropy with respect to the ion conductivity and, accordingly, have a random ion conductivity. Therefore, a solid electrochemical element is ordinarily constituted by shaping a solid electrolyte powder into a layer by pressing or into a thin film by vapor deposition and providing a pair of electrodes on both surfaces of the layer or the thin film to form one solid electrochemical element per one solid electrolyte layer.
In ordinary electrochemical elements using a liquid electrolyte, electronic and ionic contact between electrolyte and electrode material can be easily obtained. In contrast, in solid electrochemical elements constituted by solid substances, generally, it is not easy to obtain electronic and ionic contact between solid electrolytes, between electrode materials or between solid electrolyte and electrode material. In electrochemical elements using a liquid electrolyte, it is usual to add foreign matter such as a binder or the like to the electrolyte or the electrode in order to prevent leakage of the electrolyte or to prevent excessive penetration of the electrolyte into the electrode and the resulting deformation of the electrode. Meanwhile, in solid electrochemical elements, the addition of foreign matter is ordinarily avoided because it reduces said electronic and ionic contact.
If no foreign matter is used, the solid electrochemical elements, when produced in a large and thin shape, generally tend to lack in elasticity and consequently are fragile to mechanical impacts and easily destroyed or impaired.
Further, in solid electrochemical elements, the solid electrolyte generally comprises a chemically active monovalent cation as a conducting element. This monovalent cation, when exposed to oxygen or moisture in the atmosphere, is converted to a divalent cation by oxidation or immobilized in the electrolyte crystal as an oxide, whereby the conducting function of the electrolyte is lost.
Furthermore, when a plurality of solid electrochemical elements are arranged into an element group wherein they are connected in series or in parallel, it is necessary to isolate each constituent element of the element group electronically and ionically. In this case, since the electrolyte used in each element generally has random ion conductivity and has no anisotropy, each element must have an electrolyte layer ionically isolated from other electrolyte layers. Without this isolation, the ionic flow within the electrolyte of one element not only occurs between the electrodes of the element but also spreads into the electrodes of other elements, whereby the element group fails to exhibit its desired function. This is a problem when a solid electrochemical element is produced in a small or miniature size, which is a feature of solid electrochemical elements, in addition to the above-mentioned problem when a solid electrochemical element is produced in a large and thin shape. The isolation of each element in an element group requires complicated assembly steps including photolithography, etc. as used in an ordinary semiconductor assembly line.